We like our Graco Nautilus. Our 3.5yo Bear is 44inches and 45lbs. It has shoulder straps like the smaller seats, but they adjust "up" more than normal to fit bigger kids. It can be used as a booster as well. It was reasonably priced.
The Bear was climbing into the E, and then into his own seat around 2yo. He even stuff his arms thru the straps and tries to buckle himself in. I do it anyway (for safety, and 'cause I ain't got 40 min to wait.) Around 3yo he was on a "I'm gonna climb in the back" kick.....what a PITA. He'd run to the E, lift the hatch and drop the tailgate, and then scramble in.